1. Field of the Invention
The present invention relates to a zoom lens system.
2. Description of the Related Art
When an accidental shake (e.g., hand movement) is transferred to a photographic optical system, a vibration can be generated in a photographed image. There has heretofore been proposed a certain zoom lens provided with a mechanism (image stabilizing function) for compensating for the vibration of the image caused by this accidental shake in order to achieve an increased image quality over a non compensated system.
For example, an optical system (zoom lens) has been known in which a part of a lens unit constituting the optical system is moved substantially vertically to an optical axis (arranged in the horizontal direction) to compensate for the image vibration by the shake (see, Japanese Patent Application Laid-Open No. 9-230236, Japanese Patent Application Laid-Open No. 9-230237, Japanese Patent Application Laid-Open No. 10-232420 and Japanese Patent Application Laid-Open No. 10-90601).
In Japanese Patent Application Laid-Open No. 9-230236 (corresponding to U.S. Pat. No. 6,046,852), there is discussed a four-unit zoom lens comprising lens units having positive, negative, positive, and positive refractive powers in order from an object side to an image side. It is proposed in this zoom lens that the third lens unit be separated into a front lens subunit having positive refractive power and a rear lens subunit having positive refractive power, respectively. When the rear lens subunit is moved vertical to the optical axis, the image vibration is reduced (image stabilizing).
In Japanese Patent Application Laid-Open No. 9-230237 (corresponding to U.S. Pat. No. 6,266,189), there is discussed a four-unit zoom lens comprising lens units having positive, negative, positive, and positive refractive powers or a five-unit zoom lens comprising lens units having positive, negative, positive, positive, negative refractive powers, the units being arranged in order from the object side to the image side. In either of these zoom lenses, the second lens unit is separated into front and rear lens subunits, and either of the lens units is moved vertical to the optical axis to reduce the image vibration.
Moreover, in Japanese Patent Application Laid-Open No. 10-232420, there is discussed a four-unit zoom lens comprising lens units having positive, negative, positive, and positive refractive powers, which are arranged in order from the object side to the image side. In this zoom lens, during zooming, the first and third lens units are fixed, the third lens unit is separated into a lens subunit having positive refractive power and a lens subunit having negative refractive power, and either of the lens units can be moved vertical to the optical axis to reduce the image vibration.
In Japanese Patent Application Laid-Open No. 10-90601 (corresponding to U.S. Pat. No. 6,025,962), there is discussed a five-unit zoom lens comprising lens units having positive, negative, positive, negative, and positive refractive powers in order from the object side to the image side. There is described a constitution of the zoom lens in which the fourth lens unit, having a negative refractive power, is moved substantially vertical to the optical axis to compensate for the vibration of the image.
In general, in an optical system, a part of the lens units of a photographic optical system is used as image stabilizing lens unit, and the unit are disposed eccentrically in parallel in a vertical direction with respect to the optical axis to reduce the effect of image vibration.
However, an actuator can be used for moving the image stabilizing lens unit, and the generated eccentricity aberration can increase during an image stabilizing function.
For example, the image stabilizing lens unit, configured to reduce the image vibration, can have many constituting lenses, and thus the unit can have a large weight, and can have a large torque while performing electric driving. Unless the refractive power of the image stabilizing lens unit for reducing the image vibration is appropriately set, movement of the image stabilizing lens unit increases in order to obtain effects of reducing a certain amount of image vibration, and the whole optical system is enlarged.
Moreover, when the image stabilizing lens unit decenters the image, optical performances can be deteriorated in the case in which the image stabilizing lens unit is provided with a magnification varying function during the zooming, and in which a large refractive power is applied to the image stabilizing lens unit in order to raise an efficiency of the magnification varying function.
When a large refractive power is applied to the image stabilizing lens unit, there can also be a problem that eccentricity for obtaining a certain amount of reducing effects becomes excessively small, and it is difficult to drive/control the movement electrically or mechanically.